Vortex generators such as are shown in the above reference patent are well known in the art for their ability to energize the boundary layer flowing over an aerodynamic surface and to cause the air flow to remain attached to the surface. In the years when pioneer turbine aircraft were being designed, it was found that vortex generators were a quick expedient when a separation problem became apparent during flight test. Usually these problems were involved with the aircraft's flap system. However, in some aircraft, vortex generators have been used to increase the effectiveness of the rudder or other control surface which for one reason or another was not as effective as it was originally supposed to be. When the vortex generators are used in conjunction with a control surface, they usually are needed in the high lift regime only, that is, when the aircraft is moving relatively slowly and a large deflection of the control surface is required to maintain the desired flight attitude. A typical example is the rudder deflection required for a multi-engine aircraft when one of the outboard engines is inoperative thereby causing an asymmetric thrust situation. During landing this situation usually requires that the aircraft be flown at a relatively slow speed with almost the entire rudder travel being used to maintain the yaw attitude of the aircraft against the asymmetric thrust. The vortex generators are needed only during the short time the aircraft is being operated with the rudder greatly deflected. However, the drag from the vortex generators, which is substantial especially at cruise, is present during all operating modes of the aircraft. Therefore, various schemes have been proposed such as those shown in STEPHENS, U.S. Pat. No. 2,800,291 or ORNBERG, U.S. Pat. No. 3,471,107 to retract the vortex generators, extending them only during the period they might be needed. Such retracting vortex generators have not gained acceptance due to the complexity and expense of making them retractable.